It is well known to spray apply hydraulic cementitious slurries to metal structural members in order to provide a heat resistant coating thereon. U.S. Pat. Nos. 3,719,513 and 3,839,059, the disclosures of which are hereby incorporated by reference, disclose gypsum-based formulations which contain, in addition to the gypsum binder, a lightweight inorganic aggregate such as vermiculite, a fibrous substance such as cellulose and an air entraining agent. Such slurries are generally prepared at ground level and are pumped to the point of application, where they are spray applied to the substrate. Often the point of application exceeds 20 or 30 stories where high rise construction is involved. Accordingly, pumpability of the slurries is an important criteria in their formulation and preparation. Thus, they must be able to hold the large quantity of water that renders them capable of being pumped easily and to great heights, yet they must retain a consistency sufficient to prevent segregation or settling of ingredients and permit adequate yield or coverage of the substrate at a given thickness. The coating mixes must adhere to the substrate both in the slurried state and in the dry state. Also, the mix must set without undue expansion or shrinkage which could result in the formation of cracks that would seriously deter from the insulative value of the dry coating.
U.S. Pat. No. 4,751,024, the disclosure of which is incorporated herein by reference, teaches sprayable cementitious compositions containing shredded polystyrene as a lightweight aggregate in fireproofing compositions. The cementitious binder is preferably gypsum, but may instead be Portland cement. Indeed, Portland cement is typically used as the binder in applications involving high traffic areas, since the cement tends to be stronger than gypsum.
High density (40-42 pcf), high durable, cement-based structural steel fireproofing compositions are primarily used for industrial and/or exterior applications, i.e., applications in which preventing the physical failure of the composition is of the utmost importance. Accordingly, the high density product typically includes, as the hard aggregate, sand, which allows for excellent in-place and application performance. However, the sand does not contribute to the thermal characteristics of the product, and, as a result, a thicker coating is required to obtain the same hourly fireproofing protection as a product that does not include sand aggregate. That is, the sand aggregate provides physical strength to the product, but does not contribute thermally.
Reference to FIG. 1 illustrates the sacrifice in thermal performance when using a cementitious fireproofing composition that includes sand as the hard aggregate. Compositions A, B, C and D are high density (43.8 pcf, 42.2 pcf, 54.7 pcf and 48.5 pcf, respectively) compositions that include sand. Composition E is Carboline 241, available commercially from Carboline Fireproofing Products Division of RPM Company. Carboline 241 is a Portland cement based (35% by weight) product which includes muscovite (35% by weight) and aluminum hydroxide (15% by weight) as the major ingredients. It does not include sand, and has a density of 49.4 pcf. The graph in FIG. 1 illustrates the superior thermal performance of Composition E compared to the compositions utilizing sand as the hard aggregate.
It therefore would be desirable to improve the thermal performance of these and other sprayable cementitious compositions without substantially deleteriously influencing the application and physical properties thereof. The present invention is directed towards such an improvement.